The invention relates to a circuit arrangement for producing a constant voltage in a converter, particularly in the case of a flyback converter operated in a step-up mode. The invention also relates to a method for producing a constant voltage in a converter.
To keep a power that is to be converted and, hence, the thermal loading of the converter at a low level the DC isolation between the primary and the secondary of the transformer in the converter is removed and results in the circuit shown in FIG. 2. This converter produces a differential voltage between an output voltage that is to be achieved,and an input voltage applied to the input of the converter. In this arrangement, the output voltage of the converter is the result of adding the applied input voltage and the voltage produced by the converter. This converter, operated in step-up mode, is called a step-up converter.
To achieve an output voltage of +/-68 V, for example, with an input voltage applied to the input of +/-37 V, for example, the step-up converter needs to introduce a voltage of +/-31 V.
For an input voltage of +/-67 V, for example, the voltage to be readjusted by the step-up converter's converter's is +/-1 V.
However, step-up converters have the disadvantage that the output voltage cannot be kept constant if the voltage difference between the input voltage applied to its input and the output voltage becomes approximately zero.